The present invention relates to weatherable acrylonitrile-styrene-acrylate (ASA) graft copolymer compositions having a beneficial combination of impact strength and heat properties. In particular embodiments the invention relates to ASA compositions comprising a polyestercarbonate resin.
ASA resin typically has excellent weatherability and processability properties. When it is desired to make ASA formulations with higher heat properties, blends are usually prepared comprising ASA and α-methylstyrene-acrylonitrile copolymer (AMSAN) or ASA and maleimide-containing polymers. However, the maximum obtainable heat properties in such blends are rather low due to the low maximum glass transition temperature (Tg) of the materials, typically about 120° C. Furthermore, maleimide-containing polymers may have toxic properties and therefore are not suitable for many commercially applications. Better heat properties can be obtained in ASA blends with polycarbonate (PC), which latter polymer has a Tg of about 145° C. However, it is known that the addition of polycarbonate to ASA formulations can reduce the impact strength in molded articles comprising such compositions. In addition, the discoloration of these ASA-PC formulations upon weathering is usually severe due to the limited weatherability of polycarbonate. Hence, there is a continued need for ASA blends that possess an attractive balance of thermal and physical properties while retaining weatherability in molded articles.
ASA is taught as an impact modifier in compositions containing polyestercarbonate in U.S. Pat. No. 6,583,256. However, exemplary compositions also require the presence of a poly(alkylene dicarboxylate) which renders the compositions unsuitable for some applications. In particular the use of poly(alkylene dicarboxylate)s such as poly(butylene terephthalate) typically results in a composition with low impact strength and less than optimal weathering properties.